1. Field of the Invention
The present invention relates to a light scan type display device, and more particularly to the light scan type display device which may be used in the fields of AV equipment such as a TV or a video game, OA equipment such as a personal computer or a wordprocessor machine, or light information processing elements such as a light modulating element or a light operating element.
2. Description of the Related Art
To transmit a driving signal on electric wiring, in general, the wiring resistance and the floating capacitance have an adverse effect of delaying the signal waveform. In particular, an active-matrix liquid crystal display (LCD) device entails a large wiring resistance of each scan electrode and signal electrode and capacitance at an overlapped part of these electrodes. Such a large wiring resistance and capacitance may have so great an adverse effect on the display that the active-matrix LCD device may not realize a large-type display or a high-definition display. To solve the shortcoming, a light scan type display device for transmitting the driving signal with a ray of light is now being spotlighted.
As a light scan type display, the inventors of the present applicant have proposed a light scan type active-matrix LCD device prior to the present application. The liquid crystal panel provided in the light scan type active-matrix LCD device is arranged to have two substrates. One substrate has plural light waveguides ranged in the Y direction on which plural signal electrodes are ranged in the X direction. At a crosspoint between the light waveguide and the signal electrode, there is provided a switching element made of a photoconductor which is controlled by a light signal transmitted from an array of luminous elements through the light waveguide. The light switching element serves to lower its impedance when light is applied to the element so that the signal electrode may be electrically connected with the pixel electrode. When no light is applied to the element, the light switching element serves to keep its impedance high so that the signal electrode may be electrically insulated from the pixel electrode. The light scan type LCD device is driven by change of impedance of each light switching element based on the light scan signal.
If this display device is applied to a transmission type display device, the device needs to provide a backlight such as a fluorescent lamp. If the display device is applied to a projection type display device, the device needs to provide a projective lamp such as a metal halide lamp. In both the cases, the projected ray may be modified inside of the panel for implementing the image display.
The display device proposed above, however, has a shortcoming that noises caused by the projected light or natural light may be overlapped with the light signal transmitted from the array of the luminous elements unless any means is provided for preventing the projected light or the natural light from being incident to the light waveguide for transmitting a ray of light. As a result, the noises-contained scan signal reaches the switching element. The impure signal may have an adverse effect on a switching characteristic of the light switching element or cause the switching element to malfunction, thereby lowering the quality of the display.